This research is designed to determine whether obese postmenopausal women with a common polymorphism in the lipoprotein lipase (LPL) PvuII gene, i.e. the (+) allele have less favorable metabolic responses to weight loss (WL) treatment than women without the LPL PvuII cut-site (-/-). The hypothesis is that the LPL PvuII genotype affects fasting muscle and adipose tissue and LPL activity and the metabolic responses to hypocaloric feeding-induced WL in a dose-dependent manner to affect the magnitude of the reduction of total and visceral fat, and improvements in glucose/insulin and lipoprotein lipid metabolism following WL in postmenopausal women. Specific aims determine whether obese women who are homozygous for the LPL PvuII (+) cut-site, i.e. the (+/+) genotype, have greater increases in adipose tissue LPL and decreases in muscle LPL activity and larger decreases in resting metabolic rate (RMR) and fat oxidation than heterozygotes during hypocaloric diets, that are associated with: 1) the loss of less total body and visceral fat; and 2) smaller improvements in lipid and glucose metabolism than women without the cut-site, i.e., (-/-). We will study healthy, obese (Body Mass Index, 30-40 kg/m2) 50-60 year old women within 5 years of menopause. The statistical power to test our hypothesis is based on preliminary data showing differences in adipose tissue LPL responses to WL between LPL PvuII (+/+) and (-/-) genotypes, and requires 27 women/genotype. Subjects will be entered prospectively based on their LPL genotype to ensure a homogeneous group of obese menopausal women are studied to eliminate confounding factors of gender, age, duration from menopause and body composition on the metabolic responses to WL treatment. Metabolic studies are performed on prepared calculated weight maintaining eucaloric diets for 2-3 weeks at baseline and after 6-mo WL to ensure metabolic stability, and on hypocaloric diets after the short-term study to assess metabolic responses to negative energy balance. We will measure muscle and adipose tissue LPL activity, RMR, fat oxidation, total and visceral body fat (DXA and CT scans) lipoprotein lipids and. glucose/insulin responses during an oral glucose tolerance test. Following the post-WL metabolic evaluations, subjects enter a 6- mo follow-up period followed by metabolic testing to assess long- term metabolic adaptations and weight regain by genotype. Collectively, these findings will enhance our understanding of obesity by assessing the gene-metabolic mechanisms underlying the predisposition of some obese women to more favorable metabolic health benefits from WL. This would allow the targeting of WL treatments to women more likely to respond, and pharmacologic and other treatments to those less likely to respond to WL. This optimistic outcome would reduce prevalence of obesity and risk for CVD in older women.